1. Field of the Invention
The present invention pertains to a sealant and placement technique for sealing thread leaks and other relatively minute leakage points, particularly in oil and gas well tubing and casing strings.
2. Background
Oil and gas well conduits, such as casing or production tubing, frequently develop undesired fluid leakage points, such as at the threaded connections between tubing or casing sections, leaks across packers and other undesired openings. One particularly troublesome leakage problem occurs with oil wells which are being produced using gas lift. In such an arrangement, a gas, such as natural gas produced from the oil field being produced, is circulated down the casing annulus and through spaced-apart valves in the production tubing string to assist in lifting the crude oil through the tubing string. If gas leaks through the casing threaded connections into the outer annulus, serious fluid control problems may occur. In certain arctic oil wells, for example, the lifting gas may leak into an outer annulus which is filled with an insulating fluid, adversely reacting with that fluid to create voids and channels thereby destroying the insulating capability of the fluid. The leaking gas also pressurizes the wellhead, creating an operational safety hazard that requires frequent bleed-down and limiting the artificial lift gas injection pressure. Lower gas injection pressure, of course, results in reduced oil production.
Repair or replacement of casing and tubing strings to correct for leaking joints is a costly and time-consuming task. Pulling and repairing several thousand feet of tubing or casing may cost several million dollars and, of course, results in lost well production during the repair process.
One technique for repairing small holes and other leakage points in well conduits is described in U.S. Pat. No. 4,869,321, issued Sep. 26, 1989 to B. E. Hamilton. The composition and method described in the Hamilton reference is not, however, applicable to all well conduit leakage problems. The aforementioned situation wherein leakage occurs from the gas annulus through casing connections cannot benefit from the Hamilton technique or composition. One aspect of the problem of plugging small leaks is to in some way provide a sealant which may be carried into the leakage area, which may be a minute space, while at the same time being capable of plugging the leakage area. These two requirements are normally at cross purposes with one another but have been met by the unique composition and method of the present invention.